A pumice cock is a penis which has been thorougly scrubbed with a pumice rock, because of a recent sexual intercourse with a person whom you believe to have STD's. The act of "pumicing" can be applied to any part of the human body which you believe to be infected, eg. pumice anus.
ok, so i had a beer. Ok, so maybe it was more like 12. Maybe i fucked the dinnerlady from my local high-school. You know, the one who all your friends goaded you about when you were like 9 (lets just say shes no princess).
Waking up in the morning laid next to her, an overwhelming feeling of utter dispair washes over me, just like the STD's washing over my cock. I immediately leap from the bed and make my escape while sleeping beauty rests.
Arriving home i head straight for the bathroom, where i locate the pumice rock. My only logical option is to get busy with the pumice rock on my freshly diseased member.
Friend: "Dude, how many times did you fuck her last night?"
Me: "Seriously! Enough times to warrant a PUMICE COCK!!!!"